This invention relates to a return spring assembly for an engine intake throttle valve return device and, more particularly, to improvements in a spring holder sleeve for holding throttle return springs.
FIG. 4 illustrates a conventional throttle valve return device and FIGS. 5 and 6 illustrate a spring holder sleeve used in the device illustrated in FIG. 4. In these figures, reference numeral 1 designates a barrel or a throttle body, 2 is a throttle valve mounted to a valve shaft 3. 4 is a throttle lever and 6 is a stop lever which are fitted over a notched portion 3a formed at one end of the valve shaft 3 and secured by a nut 5. A return spring holder sleeve 7 is disposed on an outer circumference of a cylindrical outer end portion 3b of the valve shaft 3. As best illustrated in FIGS. 5 and 6, the spring holder sleeve 7 has a general configuration in which a flange portion 7a integrally connects an inner sleeve 7b and an outer sleeve 7c. On the outer circumferences of the inner and outer sleeves 7b and 7c, inner and outer return springs 8 and 9, respectively, are wound. The return springs 8 and 9 are torsion coil springs. One end of each of the return springs 8 and 9 is connected to the stopper lever 6 and the other end is connected to a hook 1a provided on the barrel or the throttle body 1. The outer sleeve 7c has formed therein slits 7d and 7e for allowing the end portion of the inner spring 8 to pass and extend therethrough so that the out sleeve 7c does not interfere the inner spring 8. On the end of the spring holder sleeve 7 opposite to the flange portion 7a, a partial flange 7f is provided to partially extend along the outer circumference of the outer sleeve 7c. While the outer diameters of the flanges 7a and 7f are both larger than the inner diameter of the outer coil spring 9, since the flange 7f is only circumferentially partially provided and the larger portion of the circumference is not provided with the flange 7f and a large notch 7h is defined, the outer coil spring 9 can be placed over the outer sleeve 7c through this large notch 7h.
When an accelerator pedal (not shown) is depressed, the throttle lever 4 together with the valve shaft 3 is rotated against the return torsion coil springs 8 and 9 to rotate the throttle valve 2 into an open position. When the accelerator pedal is released, the spring forces of the inner and outer torsion coil springs 8 and 9 cause the valve shaft 3 together with the throttle valve 2 to return to its closed position illustrated in FIG. 4.
With the conventional engine intake throttle valve return device of the above construction, the flange 7f of the outer sleeve 7c is only partially provided in order to allow the outer torsion coil spring 9 to be fitted over the spring holder sleeve 7. Therefore, the outer sleeve 7c has only a limited radial mechanical strength or rigidity which is not entirely satisfactory. Also, the outer torsion coil spring 9 may relatively easily be dislocated from the holder sleeve 7 when the outer spring 9 oscillates in radial direction due to the vibration of the engine for example.